Yes, Nokia 8.1 does have NFC support.
Yes, with Nokia 8.1 you can record 4K videos @ 30 fps.
Yes, Nokia 8.1 does have the HDR10 support and you can watch 4K videos on Nokia 8.1. You can record 4K videos also.
Nokia 8.1 has a double channel LPDDR4X type of 4GB RAM.